Method of sheathing spark plug electrodes



Patented Jan. 24, 1933 UNITED STATES PATENT OFFICE KENELM EDWARD LEE GUINNESS, OF LONDON, ENGLAND, ASSIGNOR 0F ONE-HALF TO K. L. G. SPARRING PLUGS LIMITED, OF LONDON, ENGLAND, A BRITISH COMPANY METHOD OF SHEATHING SPARK PLUG ELECTRODES Application filed May 23,

This invention is for improvements in or relating to sparking-plugs, and in particular to improvements in the central-electrodes of such plugs; The invention also comprises an improved method of manufacturing the central-electrodes. v

The type of central-electrode with which the invention is concerned has a head at its inner end e. the-end at which sparking takes place) and an internal insulating surface (2'. e. the surface enclosed by the external casing of the plug) composed of mica wrapping or washers.

Hitherto it has been proposed to manufacture a sparking-plug central-electrode of the above type, with a sheath of metal, having good heat-conductive properties (0. g. copper), sandwiched between the mica wrapping and the electrode proper. In this proposal a close-fitting sheath of metal complete with a wrapping of mica insulation was fitted over the electrode. Over the core thus formed were assembled mica washers with a metal collar about half way of the length of the core. When all the parts were assembled the collar was squeezed tightly to force the metal sheath into contact with the steel core of the electrode.

An object of the present invention is to provide an improved central-electrode which will have a good capacity for conducting heat away from the central sparking-tip of the plug. a

Accordingly, the present invention pro,-

vides in or for a a sparking-plug, a centralsteps of sheathing the current-conducting core with a metal of high thermal conduc- 50 tivity ('e. g. copper) by threading the sheath 1931. Serial No. 539,530.

of metal on to the core, pressing the sheath tightly into contact therewith, then apply- 'ing the mica insulation.

Conveniently, in this method, the sheath is held stationary (c. g. by pressing into a threaded end) at the end of the core remote form diameter after it has been drawn down and extended to such an extent that it has piled up against the headand after the piled up portion has been rolled into intimate contact with the head.

An embodiment of the invention will now be described with. reference to the accompanying drawing, whereon:

Figure 1 is a sectional elevation of a sparking-plug embodying a central-electrode formed in accordance with the present invention;

Figures 2, 3, 4 and 5 illustrate successive stages in the operation of sheathing the central current-conducting core of the plug with a copper-tube.

, In-Figure 1 the steel pin 10 conducting the current to the sparking-tip has a head 21 at one end and is threaded, as at 17, at

the other end to accommodate the usual terv minal .nut, not shown, which attaches the lead to the plug. The pin 10 is sheathed in a copper-tube 11 in the manner hereinafter described, and around the core so formed a number of leaves of split mica 12, are wrapped. Mica washers 13 are threaded over the core thus formed and a collar 18 maintains these mica washers in position. A further assembly of mica washers 15 surmount the collar. 18 and a nut 16 completes the assembly. The washers 1.3, the collar 18,

the washers 15, and the nut 16 are then subjected to longitudinal compression which compacts the assembly and forces the waShers 13 into close contact with the head. Thereafter, the nut 16 is crushed into engagement with the thread 17 of the pin 10 and holds the assembly referred to in compression. This formed central-electrode is fitted into an external casingQO of the plug which has the usual earthedtips 22 and is held therein a ainst the gasket 23 by the gland-nut 19. he construction thus far described is normal andtypical practice. i To attain the object of the invention it is essential that the copper-tube 11 be in intimate contact with the steel pin v and this is effected in the manner illustrated in Fig- .ures 2, 3, 4 and 5 of the drawing.

- The piece of copper-tube 11 is pressed firm- 1y onto the steel pin 10 and at the upper end He is crushed mto engagement with the threads 17 of the pin. This end is thus held stationary while the pin 10 with the tube 11 in place is pressed-into 'a series of (lies. During this operation the copper is forced into intimate contact with the steel core and at the same time is extended towards the head .21 a ainst which it piles-up as shown at 11b in igure 3 of the drawing. The iled-up I portion 11b is then rolled down, ass own at 110 in Figure'4, to bring the copper into .It will be a preciated that the method of manufacture ereinbefore described results in bringing the copper-tube 11 into intimate contact with the steel pin 10 and in particular into intimate contact with the head 21 of the said pin. After the tube has been processed in the manner described .it forms 40 an immovable part of the pin 10.

Although the above embodiment has been described with particular steps in the manufacture it will be understood that the method of bringing the copper-tube into intimate contact with the pin 10 may be varied. For example, a layer of copper may be deposited on the pin electrolytically, and this may be done in addition to the covering with the copper-tube since it is comparatively easy to obtain intimate contact between copper and copper as contrasted with intimate contact between copper and steel as efiected in the .particularexample just described. Further, although co per is the most desirable sheathing to use or the pin 10 on account of its high thermal-conductivity other metalshaving relatively high therma -conductivity may also be used.

I claim':- I

1. In a method of manufacturin central electrodes for spark plugs, the re 'minary step of sheathing a current-con ucting core having a head at the sparking end, with 'a metal of hi thermal conductivity, which as comprises g said sheath onto said core, holding said sheath stationary at the end of the core remote from the head and subjecting said sheath to a drawingprocess whereby 1t is compressed into, close contact with the core and extended into close con-- tact with the head. I I

2. In a method of manufacturing a-central electrode for a spark plug, the reliminary step of sheathing a current-con ucting core havin a head at the end at which sparkin t other end, with a sheath of metal having high thermal conductivity, which comprises3 threadin said sheath onto said core, press ing the s eath onto the threaded end so that a es place and is screw-threaded at the it 1s held stationary at that part and subjetg ing said sheath to a drawing process by mea of dies whereby it is compressed into do contact with the core and extended into close contact with the head.

3. In a method of manufacturing a central electrode of a spark plug, the reliminary step of sheathing a current-con ucting core having a head at the end at which sparking takes place with a metal of high thermal-conductivity, which comprises threading said sheath onto the core, holding said sheath stationary at the end of the core remote-from the head and subjecting said sheatn to a drawing process whereby it is compressed into close contact with the core and extended to such an'extent that it piles up against the 4. In a method ofmanufacturing a central electrode of a spark plug, the preliminary step of sheathing a current-conducting core having a head at the end at which s arkin'gtakes place with a metal of high t ermalconductivity, which comprises threadin said sheath onto the core, holding said sheat stationaryat the end of the core remote from the head, subjecting the sheath to a drawing process whereby it is compressed into close contact with the core and extended so that it piles up against the head, rolling the piled-up portion into intimate contact with the head and machinin off the compressed sheath ofmetal to a uni orm diameter-J In testimony whereof I aflix' my signature.

KENELM EDWARD Iii GUINNESS. 

